1. Field of the Iinvention
The invention relates to a cellular phone, and more particularly to a cellular phone capable of reducing electric power consumption to thereby make it possible to use a smaller-sized cell. The invention also relates to a method of controlling a lighting device of a cellular phone, which method is capable of doing the same.
2. Description of the Related Art
Since a current cellular phone makes radio signal communication, a user can use a cellular phone indoors and outdoors, even while he or she is moving. Thus, a cellular phone is now indispensable for daily life as well as for business, and is widely used day and night.
Since a cellular phone is characterized by its mobility, it is designed to include a cell or battery designed as light as possible, as a power source, and also include circuits which can operate in electric power as small as possible.
Most of cellular phones now available are designed to have a liquid crystal display device for receiving and transmitting symbol data such as a picture, a letter and other characters, as well as a function of communication originally required for a telephone. Such cellular phones are designed to include a lighting device, usually a back light device, for lighting a liquid crystal display device and/or key pads for a user to clearly read a screen of the liquid crystal display device and correctly select a desired key pad even at night or even in poor lighting circumstance.
A lighting device used for lighting a liquid crystal display device and key pads generally consumes electric power much more than electric power to be consumed by other circuits which make communication. It would be necessary for a cellular phone to include a battery having a big capacity, in order to sufficiently operate such a lighting device, which would cause a problem that a cellular phone has to be formed larger in a size, resulting in reduction in portability of a cellular phone.
In order to solve such a problem, there have been suggested a lot of attempts to minimize a size of a lighting device in a cellular phone.
For instance, a certain cellular phone is designed to include a lighting device which is tuned on when the cellular phone detects certain sound such as voice. At the same time when the lighting device is turned on, a timer equipped in the cellular phone starts its operation. When a period of time having been set in the timer has passed, the lighting device is turned off.
However, the cellular phone is accompanied with a problem that the lighting device which is now turned off might be turned on when the cellular phone is in use in noisy circumstance, resulting in failure in saving of electric power.
Japanese Unexamined Patent Publication No. 9-27844 has suggested a cellular phone which attempts to minimize a period of time in which a lighting device such as a back light device is turned on for lighting a liquid crystal display device. When it is dark, the lighting device is turned on, for instance, when a key is actuated for starting communication, or when the cellular phone receives a call. At the same time, a timer is made to start. When user""s voice is input into a speaker or when a certain period of time has passed, the lighting device is turned off.
Japanese Unexamined Patent Publication No. 9-321853 has suggested a cellular phone comprised of means for detecting start and finish of communication therethrough. When start of communication is detected, a back light device is turned off, if the back light device is turned on. When finish of communication is detected, the back light device is kept turned on in a certain period of time.
Japanese Unexamined Patent Publication No. 7-74691 has suggested a foldable cellular phone including a first plane on which dial keys are arranged and a second plane on which no dial keys are arranged. Optical sensors are formed on at least one of the first and second planes for detecting brightness therearound. When the optical sensors detect that it is dark and when a detector detects that a dial key is actuated, LED is turned on for lighting both the dial key and LCD. When the optical sensors receive light emitted from LED, the cellular phone is put into a low power consuming condition in which the cellular phone is allowed only to receive a call.
Japanese Unexamined Patent Publication No. 5-167658 has suggested a cellular phone which attempts to minimize power consumption of a battery. The cellular phone is comprised of a lighting device, an optical sensor which detects brightness therearound and transmits a detection signal when the detected brightness is lower than a threshold value, and a driver circuit which, upon receipt of the detection signal transmitted from the optical sensor, supplies electric power to the lighting device.
Japanese Unexamined Patent Publication No. 9-18564 has suggested a phone which can be used even in darkness and reduce power consumption. The phone is comprised of a lighting device, a switch through which electric power is supplied to the lighting device, first means for detecting that a man approaches the cellular phone, a first timer which controls the switch so that the lighting device is kept turned on in a certain period of time, when the first means has detected that a man approaches the cellular phone, and a second timer which controls the switch so that the lighting device is kept turned on for a second period of time, when a key is actuated while the lighting device is on.
However, it remains impossible to sufficiently reduce electric power consumption of a lighting device in a cellular phone even by the cellular phones having been suggested in the above-mentioned Publications.
It is an object of the present invention to provide a cellular phone and a method of controlling a lighting device in a cellular phone both of which are capable of reducing electric power consumption of a lighting device in a cellular phone.
In one aspect of the present invention, there is provided a cellular phone including (a) a display, (b) a key pad arrangement, (c) a lighting device which lights at least one of the display and the key pad arrangement, and (d) a controller which turns the lighting device on when the cellular phone is not in use, and turns the lighting device off when the cellular phone is in use.
There is further provided a cellular phone including (a) a display, (b) a key pad arrangement, (c) a lighting device which lights at least one of the display and the key pad arrangement, (d) a touch sensor which is turned on upon making contact with a user and transmits a first signal, and turned off upon making no contact with a user and transmits a second signal, and (e) a controller which turns the lighting device on upon receiving the second signal from the touch sensor, and turns the lighting device off upon receiving the first signal from the touch sensor.
It is preferable that the touch sensor is formed at a surface of the cellular phone. The touch sensor may be formed around a receiver of the cellular phone.
It is preferable that the cellular phone further includes a display drive circuit which drives the display, and wherein the controller turns the display drive circuit on upon receiving the second signal from the touch sensor, and turns the display drive circuit off upon receiving the first signal from the touch sensor.
In another aspect of the present invention, there is provided a method of controlling a lighting device which lights at least one of a display and a key pad arrangement in a cellular phone, including the steps of (a) turning the lighting device on while the cellular phone is not in use, and (b) turning the lighting device off while the cellular phone is in use.
There is further provided a method of controlling a lighting device which lights at least one of a display and a key pad arrangement in a cellular phone, including the steps of (a) detecting whether the cellular phone is in contact with a user, (b) turning the lighting device on while the cellular phone is not in contact with a user, and (c) turning the lighting device off while the cellular phone is in contact with a user.
It is preferable that it is detected whether the cellular phone is in contact at a surface thereof with a user in the step (a). It may be detected whether the cellular phone is in contact around a receiver of the cellular phone with a user in the step (a).
It is preferable that the cellular phone further comprises a display drive circuit which drives the display, and the display drive circuit is also turned on in the step (b) while the cellular phone is not in contact with a user, and is also turned off in the step (c) while the cellular phone is in contact with a user.
In this specification, the phrase xe2x80x9ca cellular phone is in usexe2x80x9d means a state in which a user makes communication through a cellular phone, and the phrase xe2x80x9ca cellular phone is not in usexe2x80x9d means a state in which a user does not make communication through a cellular phone though the cellular phone is turned on.
In the present invention, when the touch sensor makes no contact with a user and hence is turned on, it is deemed that the cellular phone is not in use. Whereas, when the touch sensor makes contact with a user and hence is turned off, it is deemed that the cellular phone is in use. Hence, when the lighting device is turned on in darkness for lighting a liquid crystal display device and key pad arrangement, if a user puts the cellular phone to his/her ear to hear a call, the touch sensor is turned on, and as a result, the lighting device is turned off. Thus, the present invention makes it possible to reduce electric power consumption in the lighting device.
Reduction in electric power consumption in the lighting device makes it possible to lengthen a period of time for communication and stand-by in one battery charge, and further makes it possible to reduce a battery in a size.